The effect of contamination, sediment source and salinity on the uptake, distribution, and excretion of metals by Spartina alterniflora

Spartina alterniflora, the dominant vegetation in many salt marshes, has the potential to remobilize metals (Cd, Cr, Cu, Ni, Pb, Zn) from sediment to the local salt marsh environment. My research determined the influence of sediment metal concentration, sediment type and salinity on the uptake, distribution and accumulation of metals by S. alterniflora tissues and excreted salts. Spartina alterniflora was cultivated at a constant salinity in natural and dredge sediments with three levels of metal additions (control, low, and high). The distribution and concentration of metals in S. alterniflora was influenced by both metal treatments and sediment type; however, the metals varied in their uptake and distribution. The proportional distribution of metals among tissues was influenced only by the level of metal contamination. Metal concentrations in different tissues increased with increased levels of metal contamination, but sediment type also influenced tissue concentrations. In contrast, the concentration of metals in excreted salts did not increase in response to sediment contamination, and some metals in excreted salts decreased significantly as metal contamination increased. In a concurrent experiment, S. alterniflora was cultivated in dredge sediment with a low level of metal addition at three salinities (0 psu, 15 psu, 30 psu). The distribution of Pb and Zn in tissues and excreted salts was influenced by salinity. Further analysis of the results from these experiments showed that the concentration factor (CF) and translocation factor (TF) for tissues and excreted salts varied among metals, and were significantly influenced by metal contamination. To a lesser degree, sediment type, the interaction between metal treatment and sediment type, and salinity also influenced the CFs and TFs. Additionally, the concentrations of metals in excreted salts were determined in two coastal marshes of Louisiana. The concentration of metals was much lower than the only other previously published values from New Jersey, and the cause for this discrepancy is unclear. The physiological and geochemical bases for these uptake patterns are not well understood. However, my observations illustrate the complexity of metal uptake by S. alterniflora and have potentially significant implications for the trophic transfer of metals within salt marsh food webs